1. Field of the Invention
The present invention relates to a canning structure for a catalytic converter which is a device for purifying harmful combustion gasses exhausted from internal combustion engines and the like, and to a manufacturing method thereof.
2. Description of the Related Art
Currently, ceramic honeycomb catalytic converters are widely used as automobile exhaust gas purifying devices.
Environmental issues in recent years along with even stricter exhaust gas restrictions are requiring that catalysts be able to function immediately following starting the engine when the exhaust gas is still cool, i.e., cold starts.
Accordingly, a step being taken is to reduce the thickness of the partitions of the catalyst carrier to ½ to ⅙ of the conventional thickness, so as to lower the thermal capacity of the catalyst carrier and speed up the temperature rising of the catalyst carrier, along with improving engine performance due to reductions in pressure loss.
Normally, a ceramic honeycomb catalytic converter is manufactured as shown in FIG. 4.
First, the carrier manufacturer packages a ceramic carrier 10 (ceramic honeycomb structure) which has passed inspection, and sends it to a catalyst manufacturer.
The catalyst manufacturer unpacks this, performs processes such as causing the ceramic carrier 10 (ceramic honeycomb structure) to hold the catalyst (i.e., catalyst coating), thermal processing, inspection, etc., thereby forming a catalyst carrier 25 (ceramic honeycomb catalyst carrier), which is then packaged and sent to a canning manufacturer.
The canning manufacturer unpacks this and attaches a holding material 13 to the catalyst carrier 25 so as to fix within a metal case 11 by compressed fixing (canning), thus forming a canning catalyst carrier 30, following which joining parts such as a cone portion 17 and flange 18 and the like are welded to the canning catalyst carrier 30 as necessary, thereby completing a catalytic converter 1 (ceramic honeycomb catalytic converter).
Now, in the event that a ceramic honeycomb structure having the thickness of the partitions at around ½ to ⅙ of the conventional thickness is used as the above catalyst carrier, there has been the problem that the ceramic honeycomb structure easily cracks or chips during transporting, the catalyst carrying process, the canning process, and handling in each of the processes (e.g., packaging, unpacking, placing on or taking off of the mechanical facilities (conveyers, chucking, canning, etc.)).
In order to solve this problem, the present Inventors have proposed a new ceramic honeycomb catalytic converter manufacturing process using a canning structure (an article wherein a ceramic honeycomb structure before carrying the catalyst is fixed inside a metal case beforehand, using a holding material).
However, the above canning structure has been uneconomical, since at the time of carrying the catalyst (i.e., catalyst coating), expensive catalyst is carried by not only the ceramic honeycomb structure but also the holding material which does not take part in the catalytic reaction with the exhaust gas.